Acoustical-type panels employing a honeycomb core are the subject matter of a number of patents. Thus, in U.S. Pat. No. 3,021,916 there is disclosed a panel structure comprising a honeycomb core, the cells of which are filled with loose sound deadening material such as plastic fiber, glass fiber, wool, or the like. The core is sandwiched between a perforated metal or plastic pan and a sound reflecting pan made of the same material as the perforated pan. Panels of this type are usually made by applying an adhesive to the honeycomb core and/or the inner surfaces of the pans, and, while positioned in stacked relation to one another on a hot press, pressure and heat are applied to cure the adhesive.
In U.S. Pat. No. 4,084,367, a honeycomb core is used on opposite sides of a septum or divider. The panel shown in the patent includes apertured sheet metal skins providing a single, small diameter opening in register with each cell of the split honeycomb core. The sheet metal skins are covered by a thick layer of porous sound absorbing material such as fiberglass. The entire structure is encased in a rigid metal frame formed of a plurality of channel-shaped rails. The skins are bonded to both the core and the frame to increase the rigidity and strength of the structure.
In U.S. Pat. No. 4,496,024 a sound absorbing panel is shown in which a honeycomb core has bonded to each side thereof a porous fiberglass pelt. Bonding of the pelts to the core is accomplished by placing a layer of a thermoplastic sheet material between the core and each pelt, placing the stacked layers between the upper and lower heated surfaces of a platen press, and subjecting them to pressure and heat sufficient to bring about liquification of the thermoplastic sheet material. The pressure applied to the stacked layers acts to partially press the porous pelts and the thermoplastic sheet material into the cells of the honeycomb core. The pelts are impregnated with a phenolic resin binder, and have an initial thickness of one inch. The total compressed thickness of the end product is two inches.
Yet another honeycomb cored panel is the subject matter of U.S. Pat. No. 4,522,284. The structure shown in the patent comprises a honeycomb core having a homogeneous fibrous layer bonded to each surface thereof. The fibrous layers are formed from uncured fiberglass batts impregnated with a heat curable binder. The structure is formed by assembling the honeycomb core and the uncured batts in stacked relationship, and placing them in a hot platen press. The structure is then molded to cause a surface of the batts to enter the cells of the core to impart a pillowlike configuration to the said surface. The finished panel has thickness of 1 or 2 inches.
The use of metal parts in the fabrication of acoustical-type panels as disclosed in U.S. Pat. Nos. 3,021,916 and 4,084,367 adds significantly not only to the cost of the end product, but, also the cost of manufacturing such panels. In addition, the use of metal parts in combination with non-metallic parts, coupled with the need for using a heated platen press to form an integrated structure, in the fabrication of the panels, does not render the panels adaptable to a high-speed, in-line mass production operation. The same applies with respect to the panels disclosed in U.S. Pat. Nos. 4,496,024 and 4,522,284 in that each requires the use of a heated platen press to attain a desired result. Furthermore, in the case of all of the panels shown in said patents, the mass of the panels makes them unsuitable for use as demountable panels, that is, lightweight acoustical structures which can be applied to a surface by hand pressure, using separable fastening means of the hook and loop type, for example, and which, if desired, can be demounted from said surface in the same manner without damage to the panels or the surface from which they are demounted.